Explore the feasibility to support @NamespaceAccessible

[ImJohnMDaniel]

@vazexqi mentioned in #91 the idea of supporting @NamespaceAccessible annotation in the framework. At the time, Apex did not support this annotation with interfaces. Now that the support is present in Winter21 and later, it is time again to determine if this can be accomplished.

Attention: @daveespo @afawcett @attilah

[KieranOCon]

Hi @ImJohnMDaniel, I've been following the converstion here and I really feel that this change would be of great value and probably more achievable in a shorter timeframe that trying to decide on how to package up the fflib stuff.